A control valve is a valve that issued to control conditions such as flow, pressure, or temperature by opening or closing the control valve in response to signals received from a controller. The opening or closing of a control valve may be performed by electrical, hydraulic or pneumatic actuators.
If a control valve has an unintentional obstruction (e.g., a stuck stem or a mechanical blockage) and the obstruction is not corrected, the obstruction may cause a major disruption to an operation of a plant. Similarly, if an intentional obstruction (e.g., handwheel) is left in place beyond its intended use, the plant's operation may also be seriously disrupted. It is desirable to detect and correct obstructions, both unintentional and intentional. However, only if a plant operator knows that a control valve has an obstruction can adjustments be made or maintenance performed to correct a problem with the control valve.